This invention relates to waveguide hybrid power dividers and in particular to folded hybrids.
Waveguide hybrids are commonly used in various microwave circuits, such as monopulse comparators, feed networks for antennas, waveguide switches and waveguide circulators. The most commonly known waveguide hybrid is the "magic tee", which provides colinear output waveguide ports which are opposite facing with respect to each other. There have been previously developed waveguide hybrids, using rectangular waveguide, which are "folded" in the E plane or H plane so that the colinear output ports are adjacent to each other in the E plane or the H plane.
FIG. 1 shows a typical prior art E plane folded hybrid. The hybrid has colinear output ports 10 and 12 which are adjacent to each other in the E plane, having a common H plane wall formed by a bifurcating member 14. Opposite the colinear output ports is a sum port 16, also of rectangular waveguide. Between sum port 16 and colinear output ports 10 and 12 there is a junction region 20. A difference port 18, also of rectangular waveguide is formed on the E plane wall of junction region 20.
The operation of the prior art E plane folded hybrid is illustrated in FIG. 2. In-phase wave energy signals supplied at colinear ports 10 and 12 are illustrated by solid arrows 22 and 24. When these signals reach junction region 20, where septum 14 terminates, the phase characteristics of the signals cause there to be substantially no discontinuity and there is formed a single wave energy signal represented by solid arrow 26 in junction region 20 which is transmitted past the tapered section to form an output signal 28 at sum port 16. Since the device is reciprocal in nature a wave energy signal supplied at sum port 16 will produce in-phase output signals 22 and 24 at colinear output ports 10 and 12.
Dotted arrows 30 and 32 represent out-of-phase signals supplied to colinear ports 10 and 12. Upon arriving at the end of bifurcation 14 these signals encounter a discontinuity indicated by curved dotted arrows 34 and 36 which tend to move in circular fashion within junction region 20 to form an output signal 38 in difference port 18. Difference port 18 is also reciprocal in nature and wave energy signals supplied to this port will cause there to be output signals in phase opposition illustrated by arrows 30 and 32 at colinear ports 10 and 12.
Another characteristic of the hybrid illustrated in FIGS. 1 and 2 is that colinear ports 10 and 12 are mutually isolated, as are sum and difference ports 16 and 18.
The hybrid illustrated in FIGS. 1 and 2 are typically produced using standard rectangular waveguides wherein the ratio of the H plane dimension a to the E plane dimension b is approximately 2 to 1. Consequently the combined E plane dimensions of the adjacent colinear arms c is sufficient to permit propagation of the fundamental waveguide mode in junction region 20 and difference port 18. In cases wherein the waveguide is either under-height waveguide, having a reduced b dimension, or ridge waveguide, having reduced a and b dimensions, the physical size of the junction region 20 may be physically insufficient to support the propagation of the difference mode through the junction region. While a waveguide difference port, such as difference port 18 in FIG. 1, may itself be ridge loaded to improve propagation characteristics, it is difficult to provide such ridge loading for the junction region 20 without disruption of the propagation of signals from port 16 to colinear ports 10 and 12.
It is therefore an object of the present invention to provide an E plane folded hybrid usable with waveguide having reduced cross section dimensions.
It is a further object of the invention to provide such a folded hybrid usable with ridge loaded waveguide.